1. Field of the Invention
The present invention relates to an information reading apparatus for reading information which has been recorded on an optical recording medium such as a video disk.
2. Description of the Prior Art
A conventional information reading apparatus is shown in FIG. 1. In FIG. 1, a linearly polarized laser source 2, fixed mirrors 3 and 4, a diffraction grating 5, a luminous flux enlarging lens 6, a beam splitter 7, a quarter wavelength or Q-section plate 8, movable mirrors 9 and 10, a condenser lens 11, and a light receiving element 12 are fixed on a platform 1. Under the platform 1 is an objective lens 13 and a disk 14 which serve as an optical recording medium. A laser beam, which is emitted from the linearly polarized laser source 2, is reflected by the fixed mirrors 3 and 4, passed through the beam splitter 7 and the Q-section plate 8, further reflected by the movable mirrors 9 and 10, and reaches the optical recording surface of the disk 14. The laser beam reflected from the optical recording surface of the disk 14 returns as information-carrying light by passing through the same optical path until it reaches the reflection surface 15 of the beam splitter 7. The laser beam is then reflected at the reflection surface 15 of the beam splitter 7, focused by the condenser lens 11, and converted into an electrical signal. To read efficiently from the disk 14, it is preferable to suppress the attenuation of the laser beam light as much as possible. Particularly, in the case in which the laser beam is reflected by fixed mirrors 3 and 4 for the sole purpose of changing the propagation direction of the laser beam and directing the laser beam toward the beam splitter 7, it is preferable to make every effort to prevent the amount of laser light from being unduly attenuated.